The present invention is directed generally to a method and apparatus for control of optical traps or optical tweezers. More particularly, the invention is directed to optical tweezers formed using visible light that can be used to manipulate a variety of light sensitive materials, such as living biological materials, without substantial damage or deleterious effects upon the material being investigated or manipulated.
It is known to construct optical tweezers using optical gradient forces from a single beam of light to manipulate the position of a small dielectric particle immersed in a fluid medium whose refractive index is smaller than that of the particle. The optical tweezer technique has been generalized to enable manipulation of reflecting, absorbing and low dielectric constant particles as well.
Some systems have therefore been developed which can manipulate a single particle by using a single beam of light to generate a single optical trap. To manipulate multiple particles with such systems, multiple beams of light must be employed. The difficulty of creating extended multiple-beam traps using conventional optical tweezer methodology inhibits their use in many potential commercial applications such as the inspection of biological materials generally, and also the fabrication and manipulation of nanocomposite materials including electronic, photonic and opto-electronic devices, chemical sensor arrays for use in chemical and biological assays, and holographic and computer storage matrices.
An optical tweezer uses forces exerted by an intense and tightly focused beam of light to trap and manipulate dielectric particles, typically in fluid media. Prior descriptions of optical tweezers emphasized their potential utility for biological applications such as capturing cells, or their components, for research, diagnostic evaluation, and even therapeutic purposes. These same reports also emphasized the inherent and persistent occurrence of damage or changes caused by optical trapping methods when using visible light. In particular, it has been observed that green light of wavelength xcex=514.5 nm from an Ar ion laser has caused various deleterious effects on biological material: red blood cells literally explode, the chloroplasts of green plant cells were destroyed, and the continued application of a green laser light has caused the death of trapped ciliated bacteria. Damage from the green laser light in the first two examples clearly resulted from strong absorption of green light by hemoglobin and chlorophyll, respectively, leading to rapid heating and catastrophic destruction. The mechanism of the third type of damage, dubbed xe2x80x9copticutionxe2x80x9d by those in the art, was not immediately obvious. Subsequent studies have identified optically-induced mutagensis to be a likely mechanism for the cells"" death by virtue of the use of optical tweezers.
Considerably less damage to biological materials was observed when comparable materials were optically trapped with infrared light from a Nd:YAG laser operating at xcex=1064 nm. Largely on the basis of these and similar early observations with a single optical tweezer, researchers came to the conclusion that infrared illumination is operationally superior to visible illumination for optically trapping biological materials. That is, use of infrared light did not cause any apparent deleterious effect upon biological material.
Laser-induced damage can be desirable, however, in special circumstances. For example, pulsed optical tweezers operating at xcex=532 nm have been singled out for their ability to cut biological materials, such as chromosomes. Optical tweezers used in this way are known as optical scissors or optical scalpels. Even so, the prospects for nondestructively trapping biological materials with visible light had previously been considered by those in the art to be an unacceptable method of optical trapping and manipulation due to the well documented and accepted deleterious effect on biological material.
It is therefore an object of the invention to provide an improved method and system for using at least one optical trap from light in the visible or ultraviolet portion of the spectrum.
It is also an object of the invention to provide a novel method and apparatus for control of visible light optical traps that has an increased level of efficiency, effectiveness and safety for use.
It is yet another object of the invention to provide a novel method and apparatus for control of visible light optical traps that is relatively simple to align by virtue of using light visible to the human eye.
It is still a further object of the invention to provide a novel method and apparatus for control of visible light optical traps where localized regions can be accurately trapped.
It is an additional object of the invention to provide a novel method and apparatus for control of visible light optical traps wherein the samples being manipulated are not overly heated or otherwise altered due to light absorption.
It is yet a further object of the invention to provide a novel method and apparatus for control of optical traps wherein the optical traps have highly improved tracking accuracy.
It is an another object of the invention to provide a novel method and apparatus for using visible light for optical tweezers for use on any material whose electronic, mechanical, chemical or biological state is highly sensitive to optical tweezers having a high intensity light pattern.
It is still another object of the invention to provide a novel method and apparatus for control of optical traps with a variable power level which provides efficient optical trapping but without alteration of the desired chemical, biological, electronic or mechanical state of the material.
In accordance with the above objects, it has been discovered that damage or unwanted alterations inflicted by visible optical tweezers on biological matter, and other materials sensitive to high intensity light, can be reduced to acceptable, de minimis or even zero dimensions and levels, in part through appropriate design of the optical trapping system and method. In addition, it is believed that wavelengths in the ultraviolet can also be used for particular small size objects and particular types of materials by taking advantage of the features of this invention. Consequently, such optical tweezers can have widespread applications in biological systems and other systems having light sensitive materials and possess a number of advantages over infrared optical tweezers.
Other objects, features and advantages of the present invention will be readily apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings described below wherein like elements have like numerals throughout.